1. Field of the Invention
The invention is in the field of fluid metering and dispensing.
2. Description of the Related Art
A common method of dispensing many different fluids is to apply pressure to a contained volume of the fluid at which point the fluid will flow through an available outlet valve, nozzle, or orifice. When the pressure is released, flow will cease providing that the contained volume of fluid is not compressible due to entrapped or entrained air or other gas. Optionally, the contained volume of fluid is pressurized and then released through a valve mechanism operated either manually or remotely. Flow will cease when the valve is returned to a closed position. This in turn allows any entrapped or entrained air or other gas in the fluid to compress resulting in a spurt of contained fluid on subsequent openings of the valve. A common example is dispensing caulk with a caulking gun. Other examples include grease, molding and dental impression materials, one or two part epoxies, and other adhesives, sealants, pastes, powders, compounds and fluids. In a caulking gun, a tube containing a fluid or a paste is compressed on one end by plunger powered by the action of an operator's hand. The pressure applied to the contained volume of caulk expands the somewhat elastic container and compresses any contained gases. This results in significant afterflow or run-on following removal of the operator's pressure input.
This apparatus may be sufficient for infrequent use. However, for large jobs higher viscosity fluids, increased flow rates or industrial use, muscle power is not enough. The operator would quickly become fatigued or injured from the repeated motion.
One solution that has been tried is to attach a power source to the dispenser, such as a hose with pressurized air or fluid connected, through a valve, to a cylinder or actuator which multiplies the input pressure and resultant forces so as to make dispensing easier. However, air hoses and other power sources make the dispenser difficult to handle with precision. The hoses are stiff, and act as a tether, restricting the movement of the operator. The operator often has great difficulty working against the pull of the hoses. To stop the flow in (especially) the pneumatic varieties, the pressurized air is vented to the atmosphere to pause or halt the flow of dispensed fluid. This requires large reservoirs of pressurized media to be fully functional since the pressurization is lost at each pause.
Another solution that has been tried has been to use battery packs and motors. However, batteries are expensive, heavy and burdensome; present disposal problems; and require frequent recharging for significant periods of time. In addition, neither of these solutions addresses the problem of afterflow or run-on following removal of the operator's pressure input.
What is needed, therefore, is a fluid dispensing apparatus that is both lightweight and untethered which is capable of more positive flow control and elimination of the afterflow or run-on following removal of the fluid pressure input.